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TL494: TL494 Boost output voltage spike solution

Minqi Zhao
Intellectual 1660 points
Part Number: TL494
Other Parts Discussed in Thread: UCC27517

Dear experts,

My customer is developing a boost power supply with TL494.Now they find the boost output increase and need TI's help.

  • Application background:

48Vin 72Vout 1.5kW boost power supply for motor driver. Their system is Boost (TL494+gate driver UCC27517) + Three-phase inverter bridge + synchronous motor.


  • Problem description:

Based on end customer’s need, the motor need to operate under the condition of deceleration and over rated speed. Due to these conditions, motor will generate energy flows into pre-stage boost circuit, result in boost Vout spike. During this Vout spike condition, TL494 shut down the FET and can’t control the output voltage.

Boost rated output voltage

Output under motor deceleration condition

Output under motor over rated speed condition

72V

80-90V last for 1-2s

90+V last for 10s


  • Ask for suggestions:

1. Add energy absorption circuit (3*330uF+ 35W 100) could decrease the output spike, but the cement resistance is over 90 degree of centigrade. So is the absorption circuit parameter configuration is not suitable? Or is there any better solution to solve the energy?

2. Will synchronous rectification boost circuit can solve this problem? But when down-side FET ‘s duty cycle is 0, will bootstrap driver ability be affected and can’t turn on the upper-side FET? Is there better solution to solve this kind of motor driver problem?

  • 0
    TI__Mastermind 25570 points

    Hello Minqi

    The simplest solution is to add a resistor with a controlled switch as you have shown in the diagram. The problem is that the energy is dissipated in the resistor which then gets hot - as you pointed out. This may be acceptable - it depends on what the system specifications allow.

    The other solution is to make the boost stage into a bi-directional converter so that when the output voltage increases the energy can be transferred to the source. I have not been able to find any reference design for a bi-directional converter using the TL494 so I am not sure if it can be made to work.

    Please note that if you had a bi-directional converter that the energy flows back into the 48V source and the customer would have to be sure that the source can absorb this energy before starting a bi-directional converter design.

    Please send me the commercial details for this project - Mass Production date, Annual volumes etc and I will check with some colleagues to see if we can consider designing a reference design for this type of application. Please also confirm that the source can absorb the energy - as I noted above.

    You can email the commercial details to me at

    colingillmor@ti.com

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Minqi

    We took this discussion off the forum onto emails. As such, I'm closing this thread.

    Regads

    Colin